A keyboard usually has a plurality of keys to allow a user to enter information or to activate a function in an electronic device by pressing one or more keys on the keyboard. In an electronic keyboard, keys are usually designed to cause an electrical contact in an electronic circuit when a key is pressed. The electric contact causes changes in the current or voltage in the circuit and the changes are sensed electronically in order to determine which key or keys are pressed. Some keyboards are made of optical material so that the legend under the key can be read. Some keyboards are designed so they are also used as light-guides for illumination purposes. However, the keys on those keyboards are also used to cause electrical contacts in the underlying electronic circuit.
It is desirable and advantageous to provide an optical keyboard wherein pressing the keys is mainly for changing the optical parameters of the keys.